Stepping motor volume control

gilid

Member
2002-01-25 9:28 pm
France
Has anyone tried to control a stepped attenuator via a stepping motor? I have a DIY preamp which uses a two Shallco stepped attenuators (32 positions), and I want to implement an IR remote control. Problem is that this calls for accurate, repeatable 11.25 deg rotational increments, at a decent torque.

It seems this may get very complex - I have visions of gears, clutches (to allow knob control via the front panel), etc. Anyone have any simple ideas?
 

Brett

Member
2002-01-07 6:02 pm
I thought about this a while ago when I was looking at the nice 47 position Shallcos. It never got past a thought experiment, but I think you will need a gearbox and a 200 step/rev motor. Tamiya who make all the plastic models and RC cars have gearbox sets available reasonably cheaply, and the motors are esy to get cheap surplus. I wanted a box and fine stepping for the motor so I could have each switch position be a number of steps, so if a couple were lost in the startup, it would still hit the desired position each time. The box also gives the motor a nice torque advantage.

In the end I did mine with 18 relays in a shunt, like the Pass pre's do.
 

FBJ

Member
2002-03-12 7:46 am
USA
Hey, you guys should do a search cause I remember a German web site that a member posted that builds and designs motor controls for audio step attenuators. I have the site bookmarked at home but I'm at work now and whenever I go to that web site I got an MISUSE of Company Equipment screen so I don't have it bookmark here on my work computer.

Hey Brett- my computer been misbehaving at home. I will get to those pictures of the Dynaco transformers this weekend hopefully.
 

Brett

Member
2002-01-07 6:02 pm
Hi Freddie

<b>I remember a German web site that a member posted that builds and designs motor controls for audio step attenuators.</b>

Thanks for reminding me. Would this be the one you're thinking of?
http://www.thel-audioworld.de/bauteile/regler/regler.htm

<b>Hey Brett- my computer been misbehaving at home. I will get to those pictures of the Dynaco transformers this weekend hopefully.</b>

Thank you. Whenever you get a moment'll be fine. I'm looking forward to getting them, and building the amps:)
 
motor control

I once designed a stepper control for pots, published in Audio Amateur 2/91
The idea was to use 2 single pots driven by stepper motors and some logic to implement both volume and balance functions.
(Actually they were dual pots but one section was used for position feedback).
This can easily be used with stepping attenuators IF you choose the rotational steps of the stepper motors (in degrees) equal or an integer ratio of the step size of the stepper attenuator. You then remove the indent mechanism and let the stepper motors do the discrete steps.
(If I had to build it again I would use a microcontroller like a PIC, of course, but this was 1991...)

Cheers, Jan Didden
 

FBJ

Member
2002-03-12 7:46 am
USA
Yes, Jan Didden. I had read that article in TAA many times but never had the time to build anything. Since I am at work I didn't mention it cause I couldn't remember the issuse it's in. I have been designing with the Holtek IR chips to control motorized volume and balance pots. And I have a PIC programer and basic software but no time to use any of the stuff yet with stepper motors which doesn't look to hard.
:cool:
 

MRehorst

Member
2002-05-17 8:48 pm
use solenoids?

Maybe you could use two solenoids- one that pulls clockwise one step at a time and the other pulling counterclockwise. You could put a simple ratchet gear on the shaft of the attenuator. The length of stroke of the solenoid would determine the angle the shaft rotates with each pull.

It seems like it would be pretty easy to make, especially compared to a motor setup where you're going to have problems knowing when to stop the motor for each position of the attenuator shaft.

Whether you use motors or solenoids, you're going to need some feedback into the controller to know when to stop turning the attenuator shaft.

MR
 
motor control

Mark,

Not difficult at all! Remember, a stepper motor rotates a well defined number of degrees per pulse. If that corresponds with the angle of each stepped attenuator step (sorry for the skewed language) you don't need anything like ratches, mechanical stuff etc. Just pulse the motor once, and voila, the attenuator steps exactly one position.

Other implementations are as easy: take a 24 position attenuator (that's 15 degrees right) and 7.5degree stepper motor which are widely available and you just step it 2 pulses at the time.

Alternate pulses (or as I did pairs of pulses, 1 CW and 1 CCW) give you the balance function.

If one uses a PIC microcontroller, it's easy to keep track of the positions. The beauty of this mech stuff is the inherent memory, so it comes up exactly as you turn it off.

No solenoids, for pete's sake! This is not a wharf!

Cheers, Jan Didden
 
motor control

Mark,

As an add-on to my last post, you can detect end-of-rotation on the stepper attenuator in several ways (need to do that, don't want to step CCW from min level to max level in one step, of course). With a stepped att I would add an extra deck with the end positions wired to an input of the microcontroller to detect max and min volume.

And of course, there are actually two pulse lines going to each stepper motor's chip, and their relative order determines the step direction.
 

gilid

Member
2002-01-25 9:28 pm
France
Has anyone actualy built one?

All good ideas. What I am wondering is, has anyone ever built such a beast?

Also, what is the thinking about induced noise in the audio cicuitry from all this motor control/IR circuitry? Would sheet metal shielding alone be adequate? (realizing of course, that noise induced from the steppers themselves would only be apparent during motor operation, which is not really an issue).

I too would love to see a simple stepper control circuit!
 
motor control

Yes you are right, the motors only operate when operating (huh? did I say that?), so here noise is not a problem.
The IR only works when you send a command - again, no issue as far as noise is concerned.
The ucontroller can be put to sleep, and the clock stopped, waking up if a command comes in - again, no problem.

My article describes the design using discrete logic with an IR channel which is not RC5, but RC5 should even be easier what with all the integrated xmitters and receivers available. There are tons of app notes for this.

Alternatively, you can run it from the front panel using 4 switches - vol up, vol dn, bal left, bal right.

If you know anything about PICs, converting the discrete logic to software should not be to difficult.

But, if your question is, do I have a tried and trusted design that you can copy 1-to-1, sorry, that would only take the fun out of CREATING something...


Cheers, jan Didden
 

FBJ

Member
2002-03-12 7:46 am
USA
Hey Guys, janneman's article in TAA is worth looking at. Cause not only does he have the schematics, and PCBs layout but he shows how to mount and support stepper motors in the preamp chassis. And the info is a little dated but all this can give you guys ideas on how to try other designs.
Or if you are lazy like me I would used the Holtek IR chips (transmit & recevice) loacted at www.rentron.com with schematics and PCBs for sale. And then go to a book store and look at some of the schematics in the, How to build Robots books. These books have many circuits showing schematics of motor control chips and diagrams that recevice pulses from an IR circuit to control the motors.
:cool:
 

FBJ

Member
2002-03-12 7:46 am
USA
The last sentence of my last post maybe misleading. What I meant to say saw, an IR circuit can be integrated into the motor controller circuit to supply the required pulses to the stepper motor controller chip that I have seen used to control stepper motors in robots.
:cool:
 
motor control

FBJ,

I looked at the rentron site, they have a 4 channel IR that would be a perfect match to my circuit. Remember that this has 4 logic inputs, meant for front panel switches (vol up, vol dn, bal l, bal r) but will readily accept the outputs from that IR (you may need an inverter, haven't looked at the polarity), you wouldn't need the relays either.
The only remaining thing then is to mecahnically integrate the steppers with the stepped attenuator instead of the pots, and wire the end-point contacts from the extra deck to the logic, deleting the comparators that I used to detect end of travel.
Neat, huh?

Cheers, Jan Didden
 

FBJ

Member
2002-03-12 7:46 am
USA
That's a good idea janneman,
But I got a IR remote control circuit that I designed working great with motorized pots using Holek IR chips and logic ICs. It took me many times to get the circuit to work but as far as I can tell anything works correctly. My next step is to use a PIC to control everything and the only thing keeping me from starting is time and software know how. I built a HarryHaller passive preamp with caddocks resistors and Alps black beauty pot and I must agree that I think the sound quailty equals any attenutor (to my ears).
But on another subject. I have the High Performance Regulators PCBs from Old Colony un-stuff and I know you help developed them. Are you still using these regulator boards in any of your system conponents? If so, how do these regulators still sound? Yes I know Walt Jung has a newer design in Audio Electonics 4/2000 but I want to try the older design first. Any answers would be helpful.
:cool:
 

Electro

Member
2002-04-12 4:41 am
I have used a stepper motor before. They are very simple to control and they are precised. Unipolar might be easier for you to use instead of bipolar. Stepper motors don't need a gear box because they already have enough torque

Try searching http://www.epanorama.net

Also look at http://www.howstuffworks.com/gear-ratio.htm on gear ratios.

If you hate using infrared. Go to Ramsley Electronics and pick out an RF transmitter and a reciever. Those devices looks like they can only controll one device, but with a microcontoller you can controll many devices by sending a data tranmission like a phone modem.
 
motor control

I agree.

If you want to use IR because of the ready availability of all sorts of remote control units, there is tons of info on the net for receivers and decoding by PICs. Look in the PIC areas or general IR or remote control.
Most of the PIC implementations I have seen work by counting clock pulses between received 0-1 or 1-0 transitions to determine code and address.

FBJ: yes I use these regulators in most of my projects as a matter of routine, they work great. Don't forget that any active circuit is designed with the implicit assumption that the supply is DC with a zero AC component. Any real world supply falls short of that ideal, meaning that the circuit does something else than you intended. The closer you get to an ideal supply, the more the circuit works as intended.

I like to think of a circuit as an athlete. He/she has to perform on his/her own, like running or high-jump. When the moment is there, nobody can do that for him/her. But, there is a coach, a doctor, a tech advisor, a spiritual advisor and what have you, to make sure he/she perform at the top level at the moment of truth. So it is with circuits. Give it the best support you can: first rate connectors, solid construction, high quality components, and yes, one of those super regulators....

Cheers, Jan Didden
 
Hi,

Have a look at my site. RC5 decoding routing for PIC, not by counting, but by a state-machine in the software.

I use it for a preamp to (among other things) control the motorised alps volumepot.

A previous version i once built used a disk-drive steppermotor, controlled by an 6502 processorboard. Peices of LEGO-technic to connect the steppermotor to the pot.. Good old times..
Easy to do in PIC these days..

If anyone needs more info, send me a mail.

Guido